private async Task Recover()
{
var docIdInDataFile = await _dataFile.GetLastDocId();
var docsFromWal = await _wal.ReadDocsAfter(docIdInDataFile);
await _dataFile.Apply(Tran.WithDocuments(docsFromWal));
}
public async Task AddDocuments(IReadOnlyCollection <Document> docs)
{
var tran = Tran.WithDocuments(docs);
await CommitTran(tran).ConfigureAwait(false);
}